1. Field of the Invention
The present invention relates to electrical-test equipment used for tracing conductors and finding hidden electrical elements.
2. Background of the Invention
Electrical work often requires identifying elements of a circuit or tracing a circuit behind a wall or other obstruction. For example, an electrician may wish to identify whether any electrical wiring exists or find electrical wiring attached to a particular wall outlet so that repairs may be made. By identifying hidden electrical wiring, the electrician can de-energize the circuit before exposing the wiring and performing repairs. For example, an electrician may wish to trace a hidden wire along a wall to locate a convenient place to add another outlet.
Some devices for locating and identifying electrical circuits use a transmitter and a receiver. A transmitter induces a current signal on the circuit in question. A receiver senses the induced signal. For a further description of a circuit finders using a transmitter-receiver pair, see U.S. Pat. No. 6,933,712 by Miller, et al. on Aug. 23, 2005, titled “Electrical circuit tracing and identifying apparatus and method”, the contents of which are included herein by reference.
Other sensing devices for locating and identifying electrical circuits and energized AC wiring use only a handheld receiver and rely on either changes in capacitance or a received electric field. Such devices are dependent on the environment. Such factors include the types of and dimensions of materials used in constructing the wall as well as the distance between the sensor and the wiring. These sensors operate by determining a threshold, which marks a boundary between the presence of a target and the absences of that target. The threshold is variable and is susceptible to variations in construction, thickness of the wall and subtle changes in temperature and humidity. Even the dielectric characteristics of the material used in an operator's shoes and how the operator holds the device may play a factor in the determined threshold. If an operator moves to a different floor material or the wall construction differs during operation, the determine threshold value may become ineffective and the sensor may fail to operate as intended.
In sum, the environment leads to unpredictability and uncertainty requiring careful calibration. For a sensor to have sufficient sensitivity and have the flexibility to operate in various environments, a sensor must be calibrated for that particular environment. If a sensor is not properly calibrated, the sensor may be less sensitive (e.g., if the threshold is too high) or give false-positive readings (e.g., if the threshold is too low).
The above-described conventional sensors require either a secondary transmitter or a step of threshold calibration. Therefore, a need exists to reduce or eliminate environmental variables leading to inaccurate sensor indications, thus providing an operator of a handheld sensing device with the ability to find hidden electrical wiring without relying on a secondary transmitter or reducing the emphasis placed on the initial threshold calibration step.